I have never seen anything about The Hobbit project - as a project, so to speak - ever being anything but two films. Sure, there was the idea of The Hobbit as one film, but it was unbreakably joined in the same production cycle to the "bridge film" which would "fill in" the adventure between the events of The Hobbit and the events of The Lord of the Rings. I even think that Del Toro was hired on the assumption that he would make those two films. If I remember, Jackson then announced only a few months after Del Toro came on board, that they had officially abandoned the bridge film concept, and would henceforth be working on the project as a two-film production of just The Hobbit story. Del Toro suggested that it was he who convinced Jackson and the writers that that was the way to go simply on the basis of the length and complexity of The Hobbit book. (Unconvincingly, as far as I'm concerned. It's called "adaptation". You abridge the book to make it fit the film format. Only if you are already under contract to produce two blockbuster films, and you find that the concept of one of them is fatally flawed, do you decide that the book "has to" be filmed as two features!)